1. Field of the Invention
This invention relates to a method for stabilizing organic solvents and monomers against buildup of oxidation products and to the stabilized products thereof.
2. The Prior Art
It is recognized that upon contact with oxygen (air) many organic liquids such as solvents and monomers undergo oxidation to form oxidic impurities. The most serious of these impurities are peroxides. When peroxides form in monomers such as styrene, acrylic acid and the like, they initiate and catalyze free radical polymerization of the monomer. When peroxides form in solvents such as ethers and tertiary hydrocarbons, they pose a serious hazard since the peroxides are explosive and can detonate when the solvent is heated. The problem has been especially notorious with diisopropylether.
One solution to this problem is to regularly distill solvents and/or monomers overhead from the peroxide contaminants. In both cases, this leads to expensive waste of materials, as deep bottom cuts must be taken and discarded. In the case of monomers, there is the problem that polymerization may occur within the distillation column.
The other conventional solution to this problem is to add a chemical to the solvent or monomer which inhibits the formation of undesired oxidation products such as peroxides. Typical prior art inhibitors (stabilizers) include tetraethylenepentamine p-aminophenol, and sodium diethyldithiocarbamate, all of which materials are soluble in the solvent or monomer being stabilized. While these materials are generally used in small amounts (often as little as one part per million [1 ppm] or even less), their presence in solvents or monomers can be a problem if an ultrapure solvent is required in chemical syntheses or in biological studies. In monomers, they offer the disadvantage of requiring the addition of extra catalyst or initiator to compensate for their presence. Their removal can only be effected by distillation with its inherent problems.